3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), that is, the improvement of an LTE Universal Mobile Telecommunications System (UMTS), has been introduced as 3GPP release 8. 3GPP LTE uses Orthogonal Frequency Division Multiple Access (OFDMA) in downlink and uses Single Carrier-Frequency Division Multiple Access (SC-FDMA) in uplink. 3GPP LTE adopts Multiple Input Multiple Output (MIMO) having a maximum of 4 antennas. Recently, 3GPP LTE-Advanced (LTE-A), that is, the evolution of 3GPP LTE, is being discussed.
A Minimization Drive Test (MDT) is that service providers perform a test using UE instead of a vehicle for coverage optimization. Coverage varies depending on the location of a BS, the deployment of peripheral buildings, and a user use environment. Accordingly, a service provider needs to periodically perform a driving test, and lots of costs and resources are consumed. An MDT is that a service provider measures coverage using UE.
An MDT can be divided into a logged MDT and an immediate MDT. In accordance with the logged MDT, UE performs MDT measurement and then transfers logged measurement to a network at a specific point of time. In accordance with the immediate MDT, UE performs MDT measurement and then transfers measurement to a network when a report condition is satisfied. In the logged MDT, MDT measurement is performed in an RRC idle mode, whereas in the immediate MDT, MDT measurement is performed in an RRC connected mode.
Today, as data is explosively used by users, the introduction of heterogeneous networks, such as a Closed Subscriber Group (CSG) cell, a hybrid cell, a Multimedia Broadcast and Multicast Service (MBMS)-supporting cell and/or a heterogeneous wireless communication system, such as a WLAN, is gradually increased for the purpose of traffic offloading and service differentiation. The introduction of such heterogeneous networks can result in a problem in that the complexity of a radio environment is increased, with the result that a problem in that operations related to the existing measurement/mobility of UE may not be normally performed is generated. That is, in an environment in which heterogeneous networks are mixed, there is a possibility that usage efficiency of radio resources may be deteriorated. Accordingly, there is a need for the introduction of a method capable of logging information about a heterogeneous network and reporting the information to a network such that service quality provided to UE can be optimally maintained and efficiency of radio resources can be maximized in an environment in which heterogeneous networks are mixed.